| Summary: | Changes in the stratospheric polar vortex (SPV) can remarkably impact tropospheric circulation. Based onthe diagnosis of reanalysis data, this study finds that the location shift rather than the strength change dominates the intraseasonal variability of SPV. Further analysis suggests that it coupleswell with the tropospheric circulation, forming an intraseasonal stratosphere-troposphere oscillation (STO). The STO shows periodic westward propagation throughout its lifecycle and has a deep structure extending from the troposphere to the stratosphere. It reflects the movement of the SPV toward North America, then North Pacific, Eurasia, and the North Atlantic, and causes significant changes in surface air temperature over North America and East Asia. The mechanism of the STO involves Rossby wave propagation between thetroposphere and stratosphere and cross-scale interactions in the troposphere. Upward Rossby wave propagation from thetroposphere over East Asia maintains the STO’s stratospheric component, and the reflection of these waves back to the troposphere contributes substantially to the STO’s tropospheric center over North America. Meanwhile, the linear and nonlinear processes explain the STO’s westward propagation in the troposphere, which facilities vertical wave propagationchanges. The STO unifies the SPV shifts, the retrograding tropospheric disturbances, and the wave coupling processes intoone framework and provides a holistic view for a better understanding of the intraseasonal stratosphere-troposphere coupling. Given its oscillating nature, time scale, and widespread surface response, the STO may be a potential source of predictability for the subseasonal-to-seasonal prediction.
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